A NEW lawyer for the widow of Boston Marathon bombing suspect Tamerlan Tsarnaev says his client will co-operate with investigators.

But New York lawyer Joshua Dratel said he plans to keep quiet about the details of her case publicly because that could hurt the investigation.

Mr Dratel, who has represented several terrorism suspects, joined Katherine Russell's legal team last week. He joins two Rhode Island-based lawyers who usually focus on civil cases.

Ms Russell has not been charged with any wrongdoing, but she is under intense scrutiny by the FBI as they investigate the deadly April 15 bombing, which killed three people and injured more than 260.

The authorities say the attack was carried out by her husband and his brother, Dzhokhar Tsarnaev.

Mr Dratel said yesterday that he joined Ms Russell's legal team because she needed someone who could navigate the criminal justice system and protect her interests. He said she had spoken with investigators and planned to keep co-operating.

Tamerlan Tsamaev was killed in a shootout with police (Photo: Glenn DePriest/Getty Images)

He said: "I don't see that changing in the foreseeable future. There's no inconsistency between that and her interests at this point."

Dzhokhar Tsarnaev, 19, is in a prison hospital facing charges that could bring the death penalty. Tamerlan Tsarnaev, 26, died on April 19 after a shoot-out with police.

Ms Russell, 24, had been living in Cambridge, Massachusetts, with her husband and two-year-old daughter, but has been staying with her parents in North Kingstown, Rhode Island, since the day her husband was killed. She has reverted to using her maiden name, switching from her married name of Tsarnaeva.

Among the questions about Ms Russell is what she knew or saw in the weeks leading up to the bombing, and in the days after it.

Two US officials, speaking on condition of anonymity, have said that Dzhokhar told investigators the bombs were assembled in the small apartment Ms Russell shared with her husband. One of her Rhode Island lawyers has previously said she was working long hours and was frequently away from the apartment.

Mr Dratel would not discuss details of Russell's life or relationship with her husband, and would not be specific when asked about her contact with federal investigators, such as when she had spoken with them. He said in his experience, investigators do not want people speaking to the media and publicising what they are focusing on.

"It would be counter-productive for the investigation and for Katherine's interests for us to be more forthcoming at this time with any of the details," he said. "We wouldn't want to impair the investigation in any way."